Arc flash blowout

Arc flash is quite different from electric shock. When a person gets an electric shock, effects arise from the passage of electric current through sensitive tissues, mostly nerves. Arc flash occurs when electric current passes through air. Arcs generally begin when conductors in contact and carrying high current are pulled apart.

12/01/2008


Once an arc starts, the gap fills with electrically conducting plasma and grows rapidly. Source: Coastal Training Technologies www.coastal.com

Once an arc starts, the gap fills with electrically conducting plasma and grows rapidly. Source: Coastal Training Technologies www.coastal.com

Arc flash is quite different from electric shock. When a person gets an electric shock, effects arise from the passage of electric current through sensitive tissues, mostly nerves. Arc flash occurs when electric current passes through air. Arcs generally begin when conductors in contact and carrying high current are pulled apart. Once an arc starts, the gap fills with electrically conducting plasma, and grows rapidly, especially when powered by high-voltage/low-impedance sources, such as powerlines. Any circuit energized by greater than 50 V is considered to have arc-flash potential.

 

Arc flash temperatures are limited by rapid energy loss through a number of mechanisms, including:

 

  • Radiative emission in the form of EMI/RFI, infrared, and (the biggest sink) visible light (arc flash);

  • Latent heat associated with changes of state (breaking chemical bonds, vaporizing and ionizing material in the blast zone);

  • Adiabatic expansion (arc blast).

These energy-loss mechanisms limit arc flash temperatures to “merely” a few tens of thousands of degrees Kelvin, which is still hotter than anything else on Earth. They also carry the flash’s damage beyond the arc-flash core. Injuries from arc flashes include:

 

  • Burns,

  • Temporary blindness,

  • Hearing disruption,

  • Concussion trauma, and

  • Shrapnel wounds.

Facing the danger

 

There are three strategies available to protect workers from arc flash. The first is to de-energize any electrical equipment before working on it.

 

The second is distance. The severity of possible injuries decreases with the square of the distance from the arc. If you can’t avoid working on live equipment, keep as much distance from the danger zone as possible.

 

Of course, keep non-essential personnel well away from the equipment you are working on. Establish a perimeter around the work area and keep everyone out that isn’t actively working on the equipment. That guy wearing the white shirt and tie with his hard hat shouldn’t be allowed within 15 feet of the operation — even if he is in charge of plant safety!

 

The third is protective clothing. Face shields, protective gloves, and outerwear is available from a number of industrial supply companies. Proper outerwear can prevent injury from nearly all arc flashes. For more information, do a Web search on “arc flash clothing.”

 

John Kay, engineering manager at Rockwell Automation points out that industries can address arc flash safety with both prevention and protection measures, including in-depth safety programs and new technology in electrical equipment that can redirect harmful arc flash energy away from personnel, such as relief vents in motor controllers. Other protection measures in motor control applications include NEMA low-voltage motor control centers (MCCs) with arc-containing features, such as arc-containment latches on all doors, insulation covers on the horizontal bus closing plates and automatic shutters for plug-in units.

 

Remote monitoring of motor control equipment offers uses a more sophisticated form of safety. Networked motor control devices can remotely monitor and isolate features to help prevent accidental exposure to energized parts. This technology can, for example, allow monitoring and troubleshooting without opening unit doors. Software permits real-time monitoring, configuring, and troubleshooting of both low- and medium-voltage equipment on the network from anywhere in the facility or even anywhere in the world.

 

 

Author Information
C.G. Masi is a senior editor with Control Engineering. Contact him by email at charlie.masi@reedbusiness.com

 



The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
A new approach to the Skills Gap; Community colleges may hold the key for manufacturing; 2017 Engineering Leaders Under 40
Doubling down on digital manufacturing; Data driving predictive maintenance; Electric motors and generators; Rewarding operational improvement
2017 Lubrication Guide; Software tools; Microgrids and energy strategies; Use robots effectively
The cloud, mobility, and remote operations; SCADA and contextual mobility; Custom UPS empowering a secure pipeline
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Mobility as the means to offshore innovation; Preventing another Deepwater Horizon; ROVs as subsea robots; SCADA and the radio spectrum
Power system design for high-performance buildings; mitigating arc flash hazards
Research team developing Tesla coil designs; Implementing wireless process sensing
Commissioning electrical systems; Designing emergency and standby generator systems; Paralleling switchgear generator systems

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
The maintenance journey has been a long, slow trek for most manufacturers and has gone from preventive maintenance to predictive maintenance.
Featured articles highlight technologies that enable the Industrial Internet of Things, IIoT-related products and strategies to get data more easily to the user.
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.
Maintenance Manager; California Oils Corp.
Associate, Electrical Engineering; Wood Harbinger
Control Systems Engineer; Robert Bosch Corp.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me